1. Field of the Invention
The present invention relates to a noise eliminating device for reducing a noise contained in an image signal such as a video signal, and to a program for the noise eliminating device.
2. Description of the Related Art
There exist many devices and methods for eliminating a noise from an image signal. For example, a technique is known in which a difference between a signal obtained from a certain pixel and a signal obtained from a pixel orthogonally adjacent to the certain pixel is obtained, and a value obtained by multiplying the difference by k is subtracted from the signal obtained from the certain pixel (see JP 07-184225 A, page 1, FIG. 1). According to this method, when a small difference is obtained, a probability that each of the two signals is a noise component is high, and hence a value of k is increased, while a large difference is obtained, a probability that each of the two signals is an image component is high, and hence a value of k is decreased.
In addition, a technique is known in which a plurality of noise eliminating filters, and means for detecting a horizontal edge and a vertical edge of an image signal are provided, and horizontal smoothing and vertical smoothing are carried out based on the detected horizontal edge and the detected vertical edge, respectively, thereby reducing a noise contained in an image signal (see JP 09-200579 A, page 1, FIG. 1).
However, the conventional technique involves the following problem. The conventional noise eliminating method depends on a local property of an image. Thus, the noise is reduced by filters having different characteristics. However, since the accuracy of detecting the local property is poor, the noise component is imperfectly separated from the image component due to failure in judgment or mismatching between the judgment result and the characteristics of the filters in some cases. As a result, there is encountered a problem in that the noise elimination causes new disturbance, and so forth.